Fuel injectors for injecting fuel into the combustion cylinders of an internal combustion engine are well known. These fuel injectors must deliver fuel to the combustion cylinders at the right time in the engine cycle and in the right quantity so that the engine operates smoothly at the desired speed. These fuel injectors must also discharge fuel so that the discharged fuel has the proper spray pattern and atomization since both a proper spray pattern and proper atomization are necessary in order to create the proper conditions in the combustion cylinders to assure efficient combustion of the discharged fuel.
If the fuel flow through the fuel injector fluctuates from the desired fuel flow, a proper spray pattern and proper atomization of the fuel are not created. To achieve a proper spray pattern and proper atomization of fuel, the fuel injector is conventionally arranged near the center of the combustion cylinder of the internal combustion engine so that the fuel is sprayed radially from a plurality of nozzle discharge orifices of the fuel injector. Ideally, the flow and momentum of the fuel should be such that the fuel both atomizes in the combustion cylinder and penetrates into the combustion cylinder deeply enough that it adequately mixes with air, which is also supplied to the combustion cylinder, so that efficient burning of the fuel results. If the fuel does have the correct flow and does not penetrate deeply enough, or if the fuel penetrates so deeply that it sprays the opposite end of the combustion cylinder, the fuel will neither atomize properly nor mix with the air properly to result in efficient combustion. Thus, the fuel should have a flow and a momentum vector (i.e. momentum magnitude and momentum direction) to promote the most favorable mixing conditions.
The spray pattern and atomization of the fuel which is discharged into a combustion cylinder is a function of the fuel flow through the fuel injector. Fuel injectors have been provided with the capability of adjusting and regulating the fuel flow through the fuel injectors and the discharge of fuel therefrom. Most of these fuel injectors have a plurality of discharge orifices and at most one internal variable restriction which controls the supply of fuel to the discharge orifices. This variable restriction is typically controlled by fuel pressure. Such a fuel injector cannot, therefore, vary the fuel flow rate to the nozzle discharge orifices while maintaining the fuel pressure constant. Moreover, prior fuel injectors do not allow both the volumetric flow rate and the momentum of the fuel to be independently controlled. Volumetric flow rate (e.g., in ft.sup.3 per sec) is the product of velocity of the fuel (e.g., in ft per sec) and the area (e.g., in ft.sup.2) through which the fuel flows, and momentum is the product of the mass and velocity of the fuel. Volumetric flow rate is often referred to as flow rate or simply as flow. Since flow and momentum have not been independently controlled by prior fuel injectors, the mixing rate, penetration, fuel break-up, and atomization of the fuel have not been adequate to achieve optimum fuel combustion.